The present invention relates to novel compounds and a photolithographic use of those compounds.
Photosensitive compounds usually used for the preparation of presensitized plates are the condensation products of a carbonyl compound, e.g. an aldehyde, such as formaldehyde, with a diazonium salt of a para-phenylenediamine. These condensation products are usually designated diazo resins. These resins are commonly stabilized by preparing them in the form of soluble salts of a bivalent metal, such as zinc or cadmium, with one or possibly two acid anions.
The diazonium salt of N-ethyl-N-hydroxyethyl-p-phenylenediamine has been disclosed as a weak photohardener for polyvinyl alcohol, J. Appl. Pol. Sci. Vol. 8, page 1379-1381 (1964). However, there is no suggestion in this article that the phenylenediamine diazo salt can be modified further to make a bis compound highly useful in a lithographic plate.
U.S. Pat. No. 3,778,270 describes a photosensitive composition that can be photohardened. This composition comprises a bis-diazonium photosensitive salt and a polymer that can be photocrosslinked in the presence of this bis-diazonium salt in an alkaline medium. The aforementioned photocrosslinkable polymer can be a macromolecular organic colloid comprising hydroxyl or amino groups, or a polymer such as gelatin or poly(vinyl alcohol). These photosensitive compositions are useful for the preparation of presensitized plates.
Patents relating to the background of diazonium compounds in general include U.S. Pat. Nos. 3,778,270 issued Dec. 11, 1973; 3,149,972 issued Sept. 22, 1964; British 1,453,398 published Oct. 20, 1976; German Pat. No. 1,572,108 granted Apr. 14, 1977; and Japanese Publication No. 76/034294.
The lithographic plates prepared with diazonium salts of the prior art have the disadvantage of having printing areas with insufficient affinity for greasy ink. The oleophilic property of these printing areas is not sufficiently strong and, when used on a lithographic printer, the inking of the first copies is insufficient.